


Learning Curve: Part II

by sindontquit



Category: Undertale (Video Game)
Genre: Ecto-Genitalia (Undertale), Fluff, M/M, Shower Sex, Smut
Language: English
Status: Completed
Published: 2017-06-28
Updated: 2017-06-28
Packaged: 2018-11-20 14:59:04
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,055
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11337834
Author URL: https://archiveofourown.org/users/sindontquit/pseuds/sindontquit
Summary: Fluffy, smutty fontcest. Continuation of The Learning Curve.





	Learning Curve: Part II

**Author's Note:**

> You were supposed to be showering, guys! *Dramatic sigh* 
> 
> What am I going to do with these two?

When Sans woke the following morning, everything was sticky. Fuck, everything. Blue and orange residue streaked his bones in patterns that, although extremely satisfying to look at, were quite uncomfortable now that they were dry. 

Expression torn between a grin and a grimace, Sans sat all the way up in bed. He looked down at his sleeping brother, who was collapsed on the front of his ribs and drooling into the pillow. His arms and legs were still at the awkward angles of someone who’d simply keeled over from all fours. 

The grin won out on Sans’ face. 

Moving gingerly, he scooted towards the end of the mattress before sliding off. He didn’t want to wake Papyrus. He told himself that it was simply nice to let him sleep, but if he was being honest with himself… he kind of wanted to see how long he’d knocked his energetic brother out for. 

Sans turned the handle of the door carefully before stepping out into the hallway. Reaching the bathroom, he closed the door behind him and turned the shower on. As he waited for the water to heat, he sat on the edge of the tub and examined his femurs, trying to remember when exactly each burst of color had happened. He quickly gave up. It was all just a blur of sensation-- Papyrus beneath him, melting around him, rocking his hips up to meet him. Gasping against the side of his skull. Yelping as Sans flipped him, wrapping his phalanges around the back of his little brother’s cervical vertebrae and pressing down.

Sans sighed happily, his pelvis warming at the memories. He almost regretted his decision not to wake Papyrus up. 

But he seriously needed to shower.

He stood up and stepped under the flow of the water, humming contentedly as streaks of orange and blue began to swirl into the drain. The cold tile of the wall might bother fleshier monsters, but Sans was happy to rest his arms and forehead against it as the water splashed over his bones. 

“THERE YOU ARE,” Papyrus’ voice came from behind him. Before he could turn, long arms boxed him against the shower wall. His brother pressed up against his back, skull bending forward to bite softly at his neck. Sans grinned, tilting his own skull to allow Papyrus easier access. He ground his pelvis backward gently against the taller skeleton’s. The water flowed over them both, making their bones glide against each other. 

“Sleep well, Paps?” Sans murmured. 

“THE GREAT PAPYRUS DOES EVERYTHING WELL, SANS.”

Sans chuckled. “I’ll say he does.” He turned, wrapping his arms around Papyrus’ neck and pressing their skulls together in a kiss. Papyrus leaned down to him, summoning his tongue to slide against Sans’. His long arms folded his smaller brother against him, stroking his spine. Sans moaned softly into the kiss, phalanges coming up to cup Papyrus’ face. He broke off, staring up at him, and rubbed his thumb gently against his the center of his brother’s still-outstretched tongue. 

“NNH…” 

Sans swapped his thumb for several of his fingers, shivering as Papyrus wrapped his marmalade tongue around them, sucking. With his brother’s attention on his phalanges, Sans began to step forward. Papyrus backed up until he hit the far wall of the shower, spine pressing against the cold tile. Sans withdrew his fingers, coated in slick orange magic, and ran them down the front of his brother’s sternum, leaving faint streaks on the pale slate of bone. He then wrapped his glowing blue tongue around his own fingers for a moment before reaching down to trail them gently against the tall skeleton’s pelvis. Papyrus breathed in sharply, dropping his skull back against the wall. 

As Sans leaned forward and licked a long stripe back up the sternum, the younger skeleton gasped, orange magic swirling turbulently around his pelvis where Sans continued to caress him. 

His skull continued past the top of the sternum back to Papyrus’ mouth, capturing it in another deep, heated kiss. 

“MMF!” 

Papyrus’ magic suddenly coalesced into a glowing orange cock. Sans chuckled.  
“Felt like switching it up this morning, huh, bro? Or…”  
Sans seamlessly transitioned from teasing the bones to stroking him slowly, his thumb swiping over the head.  
“...Are you just too sore to form your pussy again?”

Papyrus blushed orange, looking away shyly. His bones rattled against the white tile. “SANS… PLEASE…”

Sans grinned. “You are so fucking cute when you’re flustered, you know that? And since you’ve made such a fine cock for me…”

He locked his eyes with Papyrus’, who was biting down on a knuckle, eyes full of anticipation. Keeping his gaze fixed, Sans slowly lowered himself to his knees. Water poured over his skull, dripping from his blue tongue as he opened his mouth wide. Pressing forward, he took the head of Papyrus’ cock in his mouth. 

“OH… SANS!” 

The tall skeleton’s knees buckled slightly, one hand scrabbling desperately at the wall. Sans’ tongue cradled the underside of the orange shaft, rubbing softly. Papyrus gasped, hips bucking forward, and Sans was happy to oblige his wordless request. Blocking the flow of water with his skull, the smaller skeleton slid his tongue over every inch of his brother’s cock, slicking it up with blue magic. Finally, he summoned a magical throat and leaned in, allowing Papyrus’ member to slide in as deep as it would go. Choking lightly, he bobbed his head, fucking his own throat. 

‘OH STARS… THAT FEELS…” The tall skeleton broke off into a loud moan as Sans drew back, swirling his tongue over the head. One hand grasped at Papyrus’ iliac crest, tugging his pelvis closer to his skull, while the other snaked around to squeeze the base of his spine.

“Mmhf… mmhf… mmhf… mmhf…” Sans made happy muffled sounds around the orange cock, the constant patter of the water mingling with the slurping of his tongue and Papyrus’ moans. Papyrus had both hands on the back of his brother’s skull and was hunched over, panting.

“AHHH… YOUR MOUTH IS SO.... DON’T STOP!” 

Sans released Papyrus’ hip to attend to his own magic, which had reformed his blue pussy as soon as his knees hit the tile in front of his brother. He rubbed at his clit, rocking into his hand, letting the motion travel up his body to leverage the bobbing of his skull. Papyrus was thrusting back into his throat now, sockets squeezed shut, lost in the sensation of Sans’ tongue on his cock. Steam was beginning to cloud around them, heating the air and their bones. 

The small skeleton drew back, and Papyrus whined, canting his hips forward, trying to pull his brother’s skull back onto him. Sans resisted, waiting, staring upward. When Papyrus looked down at him in delirious confusion, he took the orange cock in his hand and licked, long and slow, up the underside, while simultaneously making sure his brother could see him slip two fingers into his aching pussy. 

“FUCK!” 

Papyrus bent suddenly forward and hooked his arms under Sans’, lifting him easily and turning to slam him against the shower wall. 

“Oh, fuck yes…” Sans’ gasp melted into a moan, the smaller skeleton wrapped his legs around his little brother’s hips, clinging to his shoulders. Reaching between them, he fumbled desperately for the orange cock, trying to line it up. Papyrus grabbed both of his brother’s delicate wrists and pinned them above his head against the wet tile, making him yelp. He used his free hand to rub his cock softly against the drenched blue folds.

Sans’ blissfully closed sockets slowly peeked open as several long moments went by and Papyrus’ cock still wasn’t sinking into him. When he met his brother’s eyes, the tall skeleton was smirking. 

“What’s…” Sans’ sockets widened, then narrowed. “Oh, you little fuckin’ tease.”

“HMMM… WHICH ONE OF US IS LITTLE AGAIN?”

Papyrus grinned mischievously and pressed him harder against the steaming tile, the tall skeleton holding his smaller brother easily in place. Sans loved it when he got like this. Papyrus’ shyness was adorable and sexy as hell, but his unexpected surges of dominance when they fucked were even hotter. Sans struggled playfully, but he was at Papyrus’ mercy, and they both knew it. The taller skeleton leaned in, licking along his brother’s cervical vertebrae. 

Sans growled, rolling his hips more urgently. “Paps, come on, fuck me already--”

“USE YOUR MANNERS, BROTHER.” Papyrus teased, the sound muffled against Sans’ neck. 

“Manners? Who the fuck taught you about manners?”

Papyrus snorted. He pulled back, head tilting to the side, and looked at his brother with gleeful surprise. It was almost too easy.

“...YOU DID, SANS.”

Papyrus expected him to laugh. Instead Sans’ eyelights blazed wide and blue with a surge of his soul and he trembled, bones rattling against the tile. The brothers’ gazes locked for a long moment, and all the years that had come before stretched between them. Love. Pride. Desire. Fear. The painful dance they had done around one another for so, so long. Bringing them, finally, to the glorious certainty of this moment. 

“Please, Paps,” Sans breathed.

Papyrus threw his weight forward and buried himself in the soft blue magic, gasping as it enveloped him. Sans arched against the tile wall with a broken cry, squeezing his legs around his baby brother’s hips. Papyrus didn’t hesitate. He thrust desperately, panting raggedly against the side of Sans’ skull. 

Sans could feel every inch of the orange cock as it pumped into him, pushing him up and down the wall at his back. The pace Papyrus set was not frantic, but rather insistent, pounding, each thrust carrying the force of his love behind it. He would show it to Sans. He would make him feel it. He was determined.

Sans keened as his magic flexed and tightened around Papyrus’, both of their voices rising as the pleasure intensified. 

“Aaah… Paps… fuck… oh, FUCK, I… please… I…”

Sans was rolling his hips, ankles crossed behind his brother’s pelvis, pulling him closer and slamming himself against each thrust. 

“SANS… SANS, I… OH, FUCK, I LOVE YOU, LOVE YOU SO MUCH…”

A gasping cry ripped from Sans’ nonexistent throat as he came around Papyrus’ twitching cock, his eyelights blown out and soul pulsing visibly in time with the trembling contractions of his walls. Papyrus felt the blue pussy quiver around him and he buried himself in it once, twice, three times before releasing with a loud moan deep in his brother’s magic. Sans felt the throbbing spurts of Papyrus’ climax and groaned, his eyelights rolling back in his skull, the phalanges of his feet curling as the sensation triggered another set of delicious aftershocks. 

Papyrus’ legs began to buckle and they slid down the wall, coming to rest on the floor of the tub. His wrists finally released, Sans wrapped his arms around his little brother, who was panting into his shoulder. Water poured down on them and Sans stared upward, transfixed, as the radiant shine of Papyrus’ soul made the falling droplets sparkle orange. 

Papyrus lifted his head and Sans turned to him, smiling breathlessly, and locked him in a passionate kiss. They lay together in the warmth of the shower, the shine from both of their souls eventually settling into a soft, even glow. The hot water ran out before they could bask for too long, however, and they wrapped one another in towels before collapsing onto Papyrus’ racecar bed. As Sans snuggled up against him, Papyrus reached over to check the time on his phone. 

NEW MESSAGE  
10:42 pm  
Undyne: Papyrus I just walked past your house why the fuck are you screaming Sans’ name like that

The tall skeleton blushed orange, then felt a sudden spike of fear. Did everyone know? What would happen to them? What if everyone hated them now? What if…

As he looked down at his drowsing brother, the grip on his soul loosened. This… having Sans in his arms… was a hard-won victory. He wasn’t about to give it up. And he wasn’t about to let anybody ruin it.  
He stroked the side of Sans’ skull gently. His small brother smiled sleepily.  
“Love you, Paps,” he murmured. 

Papyrus pressed his teeth to Sans’ forehead in a kiss, and they snoozed through the sunlit morning.


End file.
